716 MR FRANK J. COLE 



muskel folgen, dessen Verkleinerung im Querschnitt zur Verlangerung des Muskels 

 d.h. (da sein hinteres Ende fixirt ist) zu einer Vorwartsbewegung der Sehne in dem 

 engen vordern Abschnitt des Canals und Halbcanals fuhren muss." Against this view 

 must be arranged two facts : ( 1 ) the longitudinal muscle at the region of its greatest bulk 

 projects beyond the posterior extremity of the constrictor muscle ; (2) as the longitudinal 

 muscle decreases in bulk, the constrictor correspondingly increases in strength. These 

 facts, to my mind, entirely negative Furbringer's view, and rob of any point his 

 criticism of Muller's explanation, which he appears to me to misunderstand. It is also 

 difficult to see how the action of the vertical muscle can replace the constrictor 

 posteriorly so as to have a similar pushing effect on the longitudinal muscle. 1 

 however, agree with Furbringer that a movement of the ventral margin of the mouth 

 itself at the critical moment would assist in toppling the dental apparatus out of or 

 into the mouth, as the case might be. 



I took an opportunity of demonstrating this very curious mechanism to Professor 

 Sherrington, who suggested an explanation which appears to me to meet the facts of 

 the case, and to represent also what J. Muller was driving at. We may first of all 

 safely conclude that the tonic condition of the dental apparatus is one of rest, i.e. 

 that the longitudinal muscle is at most times in a state of contraction. This muscle will 

 correspond to a rapid or quick muscle which executes a movement that may be rapidly 

 repeated (withdraws the dental apparatus). The constrictor will thus correspond to a 

 sluggish or tonus muscle which preserves an attitude (maintains the tonic condition of 

 retraction). The constrictor, therefore, neither reinforces the pull of the longitudinal 

 muscle nor that of the protractors, but, on the dental apparatus reverting to its tonic 

 condition after being in action, maintains that condition, whilst the longitudinal muscle 

 becomes passive again. Consequently, when the dental apparatus is active, it is the 

 constrictor muscle that is passive (and, of course, relaxed). Similarly, the perpendicular 

 or vertical muscle is a tonus muscle, fixing the posterior end of the longitudinal muscles, 

 which project beyond the sphere of the constrictor muscle. Against this view, 

 however, I ought to state that the fibres of the longitudinal and constrictor muscles are 

 large, of the same size, aplasmic, not richly vascular, and very distinctly cross-striated. 

 Hence the morphological distinction we should expect to find has no existence, and 

 both are morphologically tonus muscles ; but as all the muscles of Myxine except the 

 velo-quadratus, velo-spinalis, cordis caudalis, and the mixed parietals are of this type, 

 this point perhaps loses in importance. I have, however, seen in at least one other 

 muscle (the copulo-tentaculo-coronarius) a few scattered plasmic fibres. 



21. M. copulo-palatinus. (Figs. 3, 9, c.pl.) 



J. MtiLLER, Heber des Zungenbeins (p. 249). Zungenbcinheber (p. 324). 

 In the case of a muscle such as this, the terms "origin" and "insertion" can only 

 have a purely arbitrary meaning, since neither termination of the muscle is a fixed point. 



